Onion

Uses

Botanical names:

Allium cepa

Parts Used & Where Grown

Like its close cousins garlic, chives, scallions, and leeks, onion is a member of the lily family (Liliaceae). It is native to Eurasia but now grows all over the world, due mostly to people bringing it with them as a staple food wherever they migrated. The French explorer Pere Marquette was saved from starvation in 1624 by eating wild onions near the present site of Chicago—the name of the city is derived from a Native American word for the odor of onions.1 The bulb of the plant is used medicinally.

Our proprietary “Star-Rating” system was developed to help you easily understand the amount of scientific support behind each supplement in relation to a specific health condition. While there is no way to predict whether a vitamin, mineral, or herb will successfully treat or prevent associated health conditions, our unique ratings tell you how well these supplements are understood by the medical community, and whether studies have found them to be effective for other people.

For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.

1 StarFor an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support.

This supplement has been used in connection with the following health conditions:

Used for

Why

2 Stars

Type 1 Diabetes

20 grams fresh onion three times per day

Large amounts of onion have been shown to lower blood sugar levels in people with diabetes, possibly by blocking the breakdown of insulin in the liver.

Preliminary trials and at least one double-blind trial have shown that large amounts of onion can lower blood sugar levels in people with diabetes.5, 6, 7 The mechanism of onion’s blood sugar-lowering action is not precisely known, though there is evidence that constituents in onions block the breakdown of insulin in the liver. This would lead to higher levels of insulin in the body.8

2 Stars

Type 2 Diabetes

20 grams fresh onion three times per day

Large amounts of onion have been shown to lower blood sugar levels in people with diabetes, possibly by blocking the breakdown of insulin in the liver.

Preliminary trials and at least one double-blind trial have shown that large amounts of onion can lower blood sugar levels in people with diabetes.9, 10, 11 The mechanism of onion’s blood sugar-lowering action is not precisely known, though there is evidence that constituents in onions block the breakdown of insulin in the liver. This would lead to higher levels of insulin in the body.12

1 Star

Asthma

Refer to label instructions

Onion may act as an anti-inflammatory in people with asthma.

Onion may act as an anti-inflammatory in people with asthma. Human studies have shown onion can be a strong anti-inflammatory.13 However, some people with asthma may experience an exacerbation of symptoms if they are allergic to onion and are exposed to it.14

Onion injections into the skin and topical onion applications have been shown to inhibit skin inflammation in people with eczema, according to one trial.

Onion injections into the skin and topical onion applications have been shown to inhibit skin inflammation in people with eczema, according to one double-blind trial.15 The quantity or form of onion that might be most effective is unknown.

1 Star

Hypertension

Refer to label instructions

Onion may have a mild blood pressure-lowering effect, according to preliminary research.

Garlic has a mild blood pressure-lowering effect, according to an analysis of ten double-blind trials.16 All of these trials administered garlic for at least four weeks, typically using 600–900 mg of garlic extract per day. Onion—closely related to garlic—may also have a mild blood pressure-lowering effect, according to preliminary research.17

Traditional Use (May Not Be Supported by Scientific Studies)

Onion has been used as food for many centuries.2 Onion was also a popular folk remedy, being applied to tumors, made into a syrup for relieving coughs, or prepared in a tincture (using gin) to relieve “dropsy” (heart failure–related edema).3 It was considered a weaker version of garlic by many herbal practitioners. Like garlic, onion has a longstanding but unsubstantiated reputation as an aphrodisiac.4

How It Works

Botanical names:

Allium cepa

How It Works

Two sets of compounds make up the majority of onion’s known active constituents—sulfur compounds, such as allyl propyl disulphide (APDS), and flavonoids, such as quercetin. Each of these groups of compounds has multiple medicinal actions.

The sulfur compounds form a strongly scented oil, particularly the compound known as thioproanal-s-oxide or lacrimatory factor. It is responsible for the tearing many people suffer while cutting onions.18 Onion and onion oil constituents have been repeatedly shown to kill various microbes in the test tube.19, 20 Studies have not been conducted in humans to determine whether onion is a useful antimicrobial agent.

APDS has been shown to block the breakdown of insulin by the liver and possibly to stimulate insulin production by the pancreas, thus increasing the amount of insulin and reducing sugar levels in the blood.21 Several uncontrolled human studies22, 23 and at least one double-blind clinical trial24 have shown that large amounts of onion can lower blood sugar levels in people with diabetes. Onion does not reduce blood sugar levels in healthy nondiabetic people.25

Sulfur compounds in onion oil have also been shown to be anti-inflammatory, both by inhibiting formation of thromboxanes and by inhibiting the action of platelet-activating factor (PAF).26, 27 Not all studies have confirmed that these actions occur in humans.28 The anti-inflammatory effect is strong enough that subcutaneous onion injections and topical onion applications inhibit skin reactions to intensely inflammatory compounds in people with or without eczema, according to the results of one double-blind study.29 Human studies have not been performed to determine whether onion would be useful in people with asthma or cough, though the anti-inflammatory action cited above suggests it might be. These actions, coupled with an ability to reduce the stickiness of platelets30 and, overall, to decrease the thickness of the blood,31 have led to interest in onion as a way to prevent or possibly reduce atherosclerosis.

Human studies have proven mixed as to whether onion is helpful for people with atherosclerosis.32 Intake of quercetin in the diet, primarily from onion, tea, and apples, has been linked to a decreased risk of having a heart attack.33 High intake of quercetin and other flavonoids from onion and other foods has been shown to decrease risk of atherosclerosis in an epidemiologic study in the United States, although the result was not considered statistically significant.34 One open clinical trial showed that a crude onion extract could lower blood pressure in some people with hypertension.35 On the whole, it is unclear whether or not onion supplements, as opposed to onions eaten as food, have a beneficial effect on heart disease.

In a preliminary study of healthy male volunteers, administration of 50 grams of raw or boiled onion prevented the rise in serum cholesterol induced by consumption of a high-fat meal.36

The evidence on cancer prevention with onion suggests a benefit for some but not necessarily for all types of cancer. Onion consumption at a level of at least half an onion a day was associated with a 50% decline in stomach cancer risk in one study.37 Higher onion intake was also correlated with lower risk of breast cancer in a French epidemiological study.38 No protective effect against colorectal cancer was seen from higher onion intake.39

How to Use It

Most human studies that have shown an effect from onions used at least 25 grams per day and often two to four times that amount.40, 41 Though some studies have found cooked onions acceptable, several studies suggest that onion constituents are degraded by cooking and that fresh or raw onions are probably most active.42, 43, 44, 45

Interactions

Botanical names:

Allium cepa

Interactions with Supplements, Foods, & Other Compounds

At the time of writing, there were no well-known supplement or food interactions with this supplement.

Interactions with Medicines

As of the last update, we found no reported interactions between this supplement and medicines. It is possible that unknown interactions exist. If you take medication, always discuss the potential risks and benefits of adding a new supplement with your doctor or pharmacist.

The Drug-Nutrient Interactions table may not include every possible interaction. Taking medicines with meals, on an empty stomach, or with alcohol may influence their effects. For details, refer to the manufacturers’ package information as these are not covered in this table. If you take medications, always discuss the potential risks and benefits of adding a supplement with your doctor or pharmacist.

Side Effects

Botanical names:

Allium cepa

Side Effects

Most people can eat onion in food without any difficulties. Higher intakes of onion may worsen existing heartburn, though it does not seem to cause heartburn in people who do not already have it.46 There are also isolated reports of allergy to onion, including among people with asthma,47manifesting as skin rash and red, itchy eyes.

Onion is safe for use in children and, in small amounts in food, during pregnancy (though some pregnant women may have heartburn that onions could exacerbate) and nursing. It is unknown whether larger amounts of onion are safe during pregnancy and nursing. One study did find that baby rats nursing from mothers that were fed onion developed a taste for onion and suffered no ill effects.48

The information presented by Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires June 2017.

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